Crustaceans and Marine Heterobranchia: A New Symbiotic Relationship in the Mediterranean Sea

The “solar-powered” Elysia timida (Risso, 1818) is an endemic Mediterranean sacoglossan living in rocky substrates at shallow water. During a scuba dive, one E. timida was photographed and collected. The observation revealed the presence of a small crustacean of the Pinnotheridae family. It was not possible to assign the crustacean to a genus, but it shares typical ecological and external morphological features with other Pinnotherinae species. This is the first report of a pea crab hosted by a non-shelled Heterobranchia and the first case of a symbiotic association between crustaceans and marine Heterobranchia reported in the Mediterranean Sea.

Molecular profiling of single neurons of known identity in two ganglia from the crabCancer borealis

Understanding circuit organization depends on identification of cell types. Recent advances in transcriptional profiling methods have enabled classification of cell types by their gene expression. While exceptionally powerful and high throughput, the ground-truth validation of these methods is difficult: If cell type is unknown, how does one assess whether a given analysis accurately captures neuronal identity? To shed light on the capabilities and limitations of solely using transcriptional profiling for cell-type classification, we performed 2 forms of transcriptional profiling—RNA-seq and quantitative RT-PCR, in single, unambiguously identified neurons from 2 small crustacean neuronal networks: The stomatogastric and cardiac ganglia. We then combined our knowledge of cell type with unbiased clustering analyses and supervised machine learning to determine how accurately functionally defined neuron types can be classified by expression profile alone. The results demonstrate that expression profile is able to capture neuronal identity most accurately when combined with multimodal information that allows for post hoc grouping, so analysis can proceed from a supervised perspective. Solely unsupervised clustering can lead to misidentification and an inability to distinguish between 2 or more cell types. Therefore, this study supports the general utility of cell identification by transcriptional profiling, but adds a caution: It is difficult or impossible to know under what conditions transcriptional profiling alone is capable of assigning cell identity. Only by combining multiple modalities of information such as physiology, morphology, or innervation target can neuronal identity be unambiguously determined.

On a parthenogenetic population of Artemia (Crustacea, Branchiopoda) from Algeria (El-Bahira, Sétif)

The brine shrimp Artemia is a small crustacean of hypersaline lakes which is commonely used in larviculture. There are parthenogenetic forms and bisexual species. The formers are from the Old World, and are the most widespread. They are known to prefer high temperatures and relatively stable environments, they are more fertile than sexual species and usually reproduce by ovoviviparity. The parthenogenetic population of Artemia from El-Bahira Lake (10 ha area), situated in the High Plateaus of Northeastern Algeria (1034 m alt), has been characterized and surveyed during two hydroperiods of 2009 and 2013. It has been found to develop only in cold seasons (winter and spring), even if the lake doesn’t dry in summer, and salinities between 46 and 127 ppt. It reproduces by oviparity and produces few cysts (5.69 ± 3.6 and 98.00 ± 28.32 offsprings/brood). Indeed, it behaves more like bisexual Mediterranean populations of A. salina than other parthenogenetic populations. Individual density was much lower during the hydroperiod of 2013, whereas fecundity was higher than in the previous hydroperiod (2009). Cyst reserve was estimated at 133.13 kg of dry weight which corresponds to a rate of 13.31 kg.ha-1

Plasticity of external setae during claw transformation in the snapping shrimp, Alpheus angulosus McClure, 2002 (Decapoda, Caridea)

The snapping shrimp, Alpheus angulosus McClure, 2002, is a small crustacean with bilaterally asymmetric claws that serve distinct behavioural and sensory functions. If the large claw is lost, the organism switches handedness, transforming its small pincer claw into a large snapping claw while simultaneously developing a small claw on the contralateral side. To better understand the mechanisms required to adapt to this radical change in body composition, we examined developmental plasticity by tracing changes in sensory setae distribution on the claws throughout transformation. We observed only two broad types of setae, simple and plumose. Quantitative analysis across molt stages revealed significant alterations in setae composition and numbers that occurred primarily on the edge of the propodus, where the most drastic morphological changes also occur. These results suggest that previous developmental mechanisms are re-engaged to support the proliferation and differentiation of new setae during transformation.

Factors influencing the diets of four morphologically divergent fish species in nearshore marine waters

The dietary compositions of Atherinomorus ogilbyi (Atherinidae), Sillago schomburgkii (Sillaginidae), Lesueurina platycephala (Leptoscopidae) and Ammotretis elongatus (Pleuronectidae) in three nearshore habitats on the lower west coast of Australia, which varied in their exposure to wave energy and the extent to which they contain sea grass, have been determined. The dietary compositions of these four abundant teleosts differed, reflecting marked differences between the location in the water column, head and mouth morphology and feeding behaviour of these species. Atherinomorus ogilbyi, which has a relatively high and large mouth, fed mainly on planktonic invertebrates in the water column, while S. schomburgkii ingested predominantly benthic prey, such as polychaetes and bivalves, which it extracted from the sediment using its downward-protruding mouth. Lesueurina platycephala employed its large mouth, cryptic coloration and ambush feeding to target relatively large teleosts and invertebrates, while the small mouth and flattened body of Ammotretis elongatus facilitated the ingestion of small crustacean prey, e.g. cumaceans and amphipods, which live on the substrate surface. Atherinomorus ogilbyi consumed predominantly calanoid copepods, cladocerans and insects during the day and mainly amphipods at night, when the latter taxon became abundant in the water column. The dietary composition of each species underwent a similar pattern of size-related change, being most pronounced in L. platycephala during the day. The diets of A. ogilbyi and S. schomburgkii, the two species for which the data were most comprehensive, differed among habitats and seasons, reflecting differences in the densities of their main prey. Comparisons between the day-time diets of the above four species with those recorded previously for a further four abundant species in the same habitats during the day, show that food resources are well distributed among the main fish species in nearshore waters along the lower west coast of Australia. This feature, together with the size-related changes in the diets of the different species, reduces the potential for inter- and intraspecific competition for food by fish species in this environment.

Computer Reconstruction of the Cellular Architecture of the Daphnia Magna Optic Ganglion

The optic ganglion of Daphnia Magna, a small crustacean that reproduces parthenogenetically contains about three hundred neurons: 110 neurons in the Lamina or anterior region and about 190 neurons in the Medulla or posterior region. The ganglion lies in the midplane of the organism and shows a high degree of left-right symmetry in its structures. The Lamina neurons form the first projection of the visual output from 176 retinula cells in the compound eye. In order to answer questions about structural invariance under constant genetic background, we have begun to reconstruct in detail the morphology and synaptic connectivity of various neurons in this ganglion from electron micrographs of serial sections (1). The ganglion is sectioned in a dorso-ventra1 direction so as to minimize the cross-sectional area photographed in each section. This area is about 60 μm x 120 μm, and hence most of the ganglion fit in a single 70 mm micrograph at the lowest magnification (685x) available on our Zeiss EM9-S.

Contributions to the Study of Relative Growth in Gammarus cheureuxi.

SUMMARYThe following two sections represent two preliminary communications to the study of relative growth in a small Crustacean admirably adapted for use as a laboratory animal in all studies involving growth and development.

XII.—The Old Red Sandstone of Shetland. Part I. South-Eastern Area. With an Account of The Fossil Fishes of the Old Red Sandstone of the Shetland Islands

The exact horizon occupied by the Shetland strata of Old Red Sandstone age, and their relation to the corresponding series in the north of Scotland, have long been subjects of considerable speculation and much uncertainty. While their resemblance to the flag-stones of Caithness and Orkney was generally recognised, more definite palæontological evidence was required for correlation purposes, and the barrenness of the islands in this respect has been commented on again and again. Up to quite recent years the only fossils found in Shetland were fragmentary plant remains of doubtful affinities, and the small crustacean Estheria membranacea; the abundant ichthyolites which characterise the beds of Caithness and Orkney seemed here to be wanting, and the dearth of fossil evidence is reflected in the conservative and guarded opinions as to the position to be assigned to the series.

V.—On a new Brachyurous Crustacean from the “Clypeus-Grit” (Inferior Oolite) of the Cotteswold Hills

In November last Mr. L. Richardson, of Cheltenham, very kindly sent me (with other fossils for inspection and determination) the carapace of a small Crustacean from the “Clypeus-Grit” of the Cotteswolds, which had been picked up and given him by Mr. C. L. Walton. As Mr. Richardson anticipated, the species proves to be new to this country, and I readily obtained his permission to describe the same.

I.—Discovery of the Remains of a Fossil Crab (Decapoda-Brachyura) in the Coal-Measures of the Environs of Mons, Belgium

M. A. Preudhomme de Borre, the Conservator of the, Royal Museum of Natural History in Brussels, having received, some time since, from M. Persenaire, the impression and counterpart of the abdomen of a small Crustacean discovered in the Coal-shales at the ‘Belle-et-Bonne’ Colliery, near Mons, he submitted it to the inspection of the Entomological Society of Brussels at their Monthly Meeting on 5th June, 1875.